System for control of brake actuator

ABSTRACT

A vehicle brake system includes a brake actuator, a brake controller operative to control the brake actuator, and at least one position sensor which senses a current position of at least one moveable brake component and provides a current position signal indicative of the current position of the at least one moveable brake component to the brake controller. The brake controller is operative to cause actuation of the brake actuator based at least in part upon a position indicative command received by the brake controller indicative of a commanded position of the at least one moveable brake component and at least in part based upon the current position signal.

FIELD OF THE INVENTION

The present invention relates to a system for controlling theapplication of a brake of a vehicle, and is particularly well-suited forcontrolling the application of an electromechanical brake withself-energizing characteristics.

BACKGROUND OF THE INVENTION

Electromechanical brakes have been known for some time. U.S. Pat. No.5,788,023 discloses a disc brake for a vehicle which can be actuatedelectrically and whose brake linings can be pressed against the brakedisc with the aid of an electric motor. The electric motor transmits itsactuation force, via a so-called planetary rolling-contact threadedspindle, onto an axially displaceably mounted piston which interactswith the brake lining.

U.S. Pat. No. 5,829,557 discloses another vehicle disc brake which canbe actuated electrically and whose brake linings can in turn be pressedagainst the brake disc by means of an electric motor serving as anactuator. The electric motor comprises a spindle gear mechanism and, bymeans of a spindle element which can be of different designs, isconnected, in the direction of displacement of the brake linings, to anaxially displaceable piston which acts on a brake lining. In thispatent, there is optional provision for the use of an additional gearmechanism for converting the torque and rotational speed.

A major problem with conventional brakes with an electric actuator isthe high actuator force which has to be applied in order to achieve asufficient braking effect. The necessary high actuator force and theresulting large power demand of the actuator make it necessary to employvery large drive units, usually electric motors, which have largetorques, and are also heavy and expensive. The result of this is thatelectromechanical brakes have, to date, not become widespread as vehiclebrakes, for example.

In order to decrease the energy consumption of the brake actuators,so-called self-energizing actuators have been proposed. Early examplesof such self-energizing brakes can be found, in U.S. Pat. Nos.4,653,614, 4,852,699, 4,946,007, 4,974,704, 5,012,901. A self-energizingbrake works according to the principle that the braking force amplifiesitself. The friction force between the brake linings and the brake discgive rise, with help of a self-energizing mechanism, to increased forceagainst the brake linings and brake disc. This increased force gives, inturn, rise to increased friction force. Hence, it is possible to produceand control large braking forces by applying relatively moderate forces.

The degree of self-energization defines the relation between the appliedforce and the actual braking force. The self-energization is stronglydependent on the disc/pad friction coefficient. Normally, the variationsin the disc/pad friction coefficient are large, and are dependent on,among other factors, the temperature of the disc and/or pad. Variationsin disc/pad friction coefficient are even possible within one and thesame brake application.

At a specific disc/pad friction coefficient, μ_(inf), the staticreinforcement of the self-energizing mechanism is principally infinity.That means that one can produce and control large brake forces by onlyapplying relatively moderate forces. For disc/pad friction coefficientslower than this specific number, the brake is stable, which means that apushing force has to be applied to produce brake forces. For disc/padfriction coefficients larger than μ_(inf), the self-energized brakeinstead will become unstable, which means that a pulling force has to beapplied to hold the brake at a specific brake force or else uncontrolledbraking (i.e., lockup) can occur.

Dimensioning the self-energizing mechanism can dimension the propertiesof the self-energized brake. There are three main ways to dimension theself-energized brake:

(1) Self-releasing brake. The self-energized brake is dimensioned sothat μ_(inf) is greater than every arising disc/pad frictioncoefficient. The brake will be self-releasing for all possible disc/padfriction coefficients. A pushing force has to be applied to accomplishbrake forces.

(2) Self-applying brake. The self-energized brake is dimensioned so thatμ_(inf) is lower than all possible disc/pad friction coefficients. Thebrake will be self-applying for all possible disc/pad frictioncoefficients. A pulling force has to be applied to hold the brake at aspecific brake force.

(3) Self-releasing or self-applying brake. The self-energized brake isdimensioned so that the disc/pad friction coefficient can be bothgreater and lower than μ_(inf), hence it can be active in both theself-releasing and the self-applying domains. (A special case is todimension the brake so that μ_(inf) is around the nominal value for thedisc/pad friction coefficient. The average degree of self-energizationis then maximized under normal conditions.) The brake will beself-releasing when the disc/pad friction coefficients are lower thanμ_(inf), and self-applying when the disc/pad friction coefficients aregreater than μ_(inf).

In cases (2) and (3) above, control based on feedback is criticallynecessary to stabilize the brake. Otherwise the self-energized brake maybecome unstable, resulting in uncontrollable braking (i.e., lockup). Onealternative is to pull back the brake (without feedback) when sensorsnormally used for the feedback are detected to be not functioningproperly. However, in this case, it is no longer possible to maintainany brake functionality. Further, the brake actuator reinforcementvaries extensively when the disc/pad friction coefficient changes.Without control, the variations in brake force would be extensive. It isalso necessary to achieve the correct commanded torque/force on allbrakes on each axle of the vehicle (unless it is specifically desiredthat they not be the same, for example during ABS). This is important sothat the brake torque/force will not become different on the differentwheels at the same commanded brake torque/force.

U.S. Pat. No. 6,318,513 discloses an electromechanical brake whichincludes an arrangement which brings about self-energization of theactuation force generated by the electric actuator. The brake alsoincludes a device for comparing a setpoint value of a frictional forcewith the actual value of the frictional force, which device, in theevent of a deviation of the actual value from the setpoint value, drivesthe electric actuator to correspondingly increase or reduce thegenerated actuation force, and thus approximates the actual value to thesetpoint value of the frictional force. However, controlling theelectric actuator based upon feedback indicative of the frictional forceis disadvantageous for a number of reasons.

One such disadvantage of this configuration becomes apparentparticularly when a disc has a thickness that varies during arevolution, which is a quite normal case. This leads to a varyingmeasured clamp or frictional force with a frequency proportional to thewheel rotation speed and the amplitude directly proportional to thebrake actuator stiffness. A direct clamp or frictional force feedbackwould try to compensate for the force error caused by the disc thicknessvariation. At some vehicle speed this will lead to a high energyconsumption compared to an open-loop system as in today's pneumaticsystem where the disc thickness variations would be uncompensated by thecontrol loop.

Another disadvantage relates to the fact that a typical brake caliperincludes a brake actuator working against the disc on one side of thecaliper arrangement and with a number of sliding pins to equalize theforce between this side of the disc and the other where a fixed pad islocated. This is typically known as a “floating caliper” design, and isquite common. Due to ageing and corrosion the sliding pin function maybe far from ideal, particularly at the end of the life-cycle of thebrake actuator. This may lead to higher static friction of the slidingpins which can cause a slip-stick effect on the equalization of theforce between the two sides of the disc. The stick-slip effect may leadto an unstable force sensor signal. Experience shows that introducingthis type of signal in a feedback loop may cause problems in the controlloop, especially when working at the optimum degree ofself-energization.

A further disadvantage relates to the fact that when controlling theself-energized brake actuator with a disc/pad friction coefficient closeto the friction coefficient when the static reinforcement is infinity,μ_(inf), the backlash in the mechanical transmission may be taken intoaccount in control calculations. In the mechanical link between thecontrolling force/torque from the motor to the clamping force of thepad/disc it is difficult and costly to totally eliminate the backlash inthe mechanical transmission. The characteristics of the self-energizedbrake actuator in the infinite reinforcement region combined with abacklash in the mechanical transmission in the control loop will reducethe performance of the control loop, and it will increase the dissipatedenergy from responding to disturbances resulting from the backlash. Inorder to use the full advantage of the self-energization principle, itis important to use a control strategy that allow a fast and energyefficient way to control the brake actuator also in the infinitereinforcement region. As such, taking the backlash in the mechanicaltransmission into account in the control calculations is undesirable.

What is desired, therefore, is a system for controlling application ofan electronically controlled brake which is well-suited for controllingthe application of an electromechanical brake with self-energizingcharacteristics, which facilitates the stability of a self-energizingbrake for all possible disc/pad friction coefficients, which achievesthe correct commanded torque/force on all brakes on the vehicle, whichrelies on sensor feedback to control application of the brake, whichrelies on sensor feedback indicative of other than the frictional forcebetween the disc and pad, clamping force of the caliper or brake torque,which is not substantially deleteriously affected by a disc which has athickness that varies during a revolution, which is not substantiallydeleteriously affected by ageing and corrosion of the sliding pins in afloating caliper design, and which does not take into account backlashin the mechanical transmission in control calculations.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide asystem for controlling application of an electronically controlled brakewhich is well-suited for controlling the application of anelectromechanical brake with self-energizing characteristics.

Another object of the present invention is to provide a system forcontrolling application of an electronically controlled brake having theabove characteristics and which facilitates the stability of aself-energizing brake for all possible disc/pad friction coefficients.

A further object of the present invention is to provide a system forcontrolling application of an electronically controlled brake having theabove characteristics and which achieves the correct commandedtorque/force on all brakes on the vehicle.

Still another object of the present invention is to provide a system forcontrolling application of an electronically controlled brake having theabove characteristics and which relies on sensor feedback to controlapplication of the brake.

Yet a further object of the present invention is to provide a system forcontrolling application of an electronically controlled brake having theabove characteristics and which relies on sensor feedback indicative ofother than the frictional force between the disc and pad, clamping forceof the caliper or brake torque.

Still a further object of the present invention is to provide a systemfor controlling application of an electronically controlled brake havingthe above characteristics and which is not substantially deleteriouslyaffected by a disc which has a thickness that varies during arevolution.

Still yet another object of the present invention is to provide a systemfor controlling application of an electronically controlled brake havingthe above characteristics and which is not substantially deleteriouslyaffected by ageing and corrosion of the sliding pins in a floatingcaliper design.

Yet still a further object of the present invention is to provide asystem for controlling application of an electronically controlled brakehaving the above characteristics and which does not take into accountbacklash in the mechanical transmission in control calculations.

These and other objects of the present invention are achieved in oneembodiment of the present invention by provision of a vehicle brakesystem which includes a brake actuator, a brake controller operative tocontrol the brake actuator, and at least one position sensor whichsenses a current position of at least one moveable brake component andprovides a current position signal indicative of the current position ofthe at least one moveable brake component to the brake controller. Thebrake controller is operative to cause actuation of the brake actuatorbased at least in part upon a position indicative command received bythe brake controller indicative of a commanded position of the at leastone moveable brake component and at least in part based upon the currentposition signal.

In some embodiments, the brake actuator comprises a self-energizingbrake actuator. In some embodiments, the brake actuator comprises anelectromechanical brake actuator, actuation of which is at leastpartially achieved employing an electric motor. In certain of theseembodiments, the at least one moveable brake component comprises anoutput shaft of the electric motor. In certain of these embodiments, theoutput shaft is rotatably moveable, the current position signal isindicative of the current rotational position of the output shaft, andthe position indicative command is indicative of a commanded rotationalposition of the output shaft.

In some embodiments, the at least one moveable brake component comprisesat least one of a brake pad and a brake pad carrier. In certain of theseembodiments, the at least one of a brake pad and a brake pad carrier isaxially moveable, the current position signal is indicative of thecurrent axial position of the at least of a brake pad and a brake padcarrier, and the position indicative command is indicative of acommanded axial position of the at least of a brake pad and a brake padcarrier.

In some embodiments, the system further includes a command converter forconverting a primary command into the position indicative command. Incertain of these embodiments, the primary command comprises at least oneof a commanded brake torque, a commanded friction force and a commandedclamping force. In some embodiments, the command converter employs atleast one of an effective disc brake radius parameter, a pad/disccoefficient of friction parameter, a brake elasticity parameter, and aslack position parameter in order to convert the primary command intothe position indicative command.

In some embodiments, the system further includes a parameter estimatorfor estimating, based upon sensor input, at least one parameter used bythe command converter to convert the primary command into the positionindicative command, and for supplying the estimated parameter to thecommand converter. In certain of these embodiments, the at least oneparameter comprises at least one of an effective disc brake radiusparameter, a pad/disc coefficient of friction parameter, a brakeelasticity parameter, and a slack position parameter. In certainembodiments, the sensor input is indicative of at least one of thefollowing: a clamping force, a friction force, a brake torque, thecurrent position of the at least one moveable brake component, avelocity of a brake disc, an acceleration of a brake disc, a motorcurrent, a motor voltage and a motor torque.

According to another embodiment of the present invention, a vehiclebrake system includes an electromechanical self-energizing brakeactuator, actuation of which is at least partially achieved employing anelectric motor, a brake controller operative to control the brakeactuator, at least one position sensor which senses a current positionof at least one moveable brake component and provides a current positionsignal indicative of the current position of the at least one moveablebrake component to the brake controller, a command converter forconverting a primary command into a position indicative commandindicative of a commanded position of the at least one moveable brakecomponent and providing the position indicative command to the brakecontroller, and a parameter estimator for estimating, based upon sensorinput, at least one parameter used by the command converter to convertthe primary command into the position indicative command, and forsupplying the estimated parameter to the command converter. The brakecontroller is operative to cause actuation of the brake actuator basedat least in part upon the position indicative command received by thebrake controller and at least in part based upon the current positionsignal.

In some embodiments, the at least one moveable brake component comprisesan output shaft of the electric motor. In certain of these embodiments,the output shaft is rotatably moveable, the current position signal isindicative of the current rotational position of the output shaft, andthe position indicative command is indicative of a commanded rotationalposition of the output shaft. In some embodiments, the at least onemoveable brake component comprises at least one of a brake pad and abrake pad carrier. In certain of these embodiments, the at least one ofa brake pad and a brake pad carrier is axially moveable, the currentposition signal is indicative of the current axial position of the atleast of a brake pad and a brake pad carrier, and the positionindicative command is indicative of a commanded axial position of the atleast of a brake pad and a brake pad carrier.

In some embodiments, the primary command comprises at least one of acommanded brake torque, a commanded friction force and a commandedclamping force. In certain of these embodiments, the command converteremploys at least one of an effective disc brake radius parameter, apad/disc coefficient of friction parameter, a brake elasticityparameter, and a slack position parameter in order to convert theprimary command into the position indicative command. In someembodiments, the at least one parameter comprises at least one of aneffective disc brake radius parameter, a pad/disc coefficient offriction parameter, a brake elasticity parameter, and a slack positionparameter. In certain of these embodiments, the sensor input isindicative of at least one of the following: a clamping force, afriction force, a brake torque, the current position of the at least onemoveable brake component, a velocity of a brake disc, an acceleration ofa brake disc, a current of the motor, a voltage of the motor and atorque of the motor.

In another respect, the present invention relates to a method ofcontrolling a vehicle brake including the steps of receiving a currentposition signal indicative of a current position of at least onemoveable brake component, receiving a position indicative commandindicative of a commanded position of the at least one moveable brakecomponent, and causing actuation of a brake actuator based at least inpart upon the position indicative command and at least in part basedupon the current position signal.

In some embodiments, the brake actuator comprises a self-energizingbrake actuator. In some embodiments, the brake actuator comprises anelectromechanical brake actuator, actuation of which is at leastpartially achieved employing an electric motor. In certain of theseembodiments, the at least one moveable brake component comprises anoutput shaft of the electric motor. In some embodiments, the outputshaft is rotatably moveable, the current position signal is indicativeof the current rotational position of the output shaft, and the positionindicative command is indicative of a commanded rotational position ofthe output shaft.

In some embodiments, the at least one moveable brake component comprisesat least one of a brake pad and a brake pad carrier. In certain of theseembodiments, the at least one of a brake pad and a brake pad carrier isaxially moveable, the current position signal is indicative of thecurrent axial position of the at least of a brake pad and a brake padcarrier, and the position indicative command is indicative of acommanded axial position of the at least of a brake pad and a brake padcarrier.

In some embodiments, the method further includes the step of convertinga primary command into the position indicative command. In certain ofthese embodiments, the primary command comprises at least one of acommanded brake torque, a commanded friction force and a commandedclamping force. In some embodiments, the converting step employs atleast one of an effective disc brake radius parameter, a pad/disccoefficient of friction parameter, a brake elasticity parameter, and aslack position parameter in order to convert the primary command intothe position indicative command.

In some embodiments, the method further includes the step of estimating,based upon sensor input, at least one parameter used during theconverting step to convert the primary command into the positionindicative command. In certain of these embodiments, the at least oneparameter comprises at least one of an effective disc brake radiusparameter, a pad/disc coefficient of friction parameter, a brakeelasticity parameter, and a slack position parameter. In someembodiments, the sensor input is indicative of at least one of thefollowing: a clamping force, a friction force, a brake torque, thecurrent position of the at least one moveable brake component, avelocity of a brake disc, an acceleration of a brake disc, a motorcurrent, a motor voltage and a motor torque.

In a further embodiment of the present invention, a method ofcontrolling a vehicle brake includes the steps of receiving a primarycommand, converting the primary command into a position indicativecommand indicative of a commanded position of at least one moveablebrake component, estimating, based upon sensor input, at least oneparameter used during the converting step to convert the primary commandinto the position indicative command, receiving a current positionsignal indicative of a current position of the at least one moveablebrake component, and causing actuation of a self-energizing brakeactuator based at least in part upon the position indicative command andat least in part based upon the current position signal.

In some embodiments, the brake actuator comprises an electromechanicalbrake actuator, actuation of which is at least partially achievedemploying an electric motor. In certain of these embodiments, the atleast one moveable brake component comprises an output shaft of theelectric motor. In some embodiments, the output shaft is rotatablymoveable, the current position signal is indicative of the currentrotational position of the output shaft, and the position indicativecommand is indicative of a commanded rotational position of the outputshaft.

In some embodiments, the at least one moveable brake component comprisesat least one of a brake pad and a brake pad carrier. In certain of theseembodiments, the at least one of a brake pad and a brake pad carrier isaxially moveable, the current position signal is indicative of thecurrent axial position of the at least of a brake pad and a brake padcarrier, and the position indicative command is indicative of acommanded axial position of the at least of a brake pad and a brake padcarrier.

In some embodiments, the primary command comprises at least one of acommanded brake torque, a commanded friction force and a commandedclamping force. In certain embodiments, the converting step employs atleast one of an effective disc brake radius parameter, a pad/disccoefficient of friction parameter, a brake elasticity parameter, and aslack position parameter in order to convert the primary command intothe position indicative command. In some embodiments, the at least oneparameter comprises at least one of an effective disc brake radiusparameter, a pad/disc coefficient of friction parameter, a brakeelasticity parameter, and a slack position parameter. In someembodiments, the sensor input is indicative of at least one of thefollowing: a clamping force, a friction force, a brake torque, thecurrent position of the at least one moveable brake component, avelocity of a brake disc, an acceleration of a brake disc, a motorcurrent, a motor voltage and a motor torque.

The invention and its particular features and advantages will becomemore apparent from the following detailed description considered withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one embodiment of a brake systemincorporating a system for controlling the application of a brake of avehicle in accordance with the present invention;

FIG. 2 is a schematic view of another embodiment of a brake systemincorporating a system for controlling the application of a brake of avehicle in accordance with the present invention;

FIG. 3 is a schematic view illustrating in simplified terms theprinciples behind the operation of the brake system of FIG. 2;

FIG. 4 is a block diagram illustrating in more detail the system forcontrolling the application of a brake of a vehicle shown in FIGS. 1 and2;

FIG. 5 is a block diagram illustrating in more detail a commandconversion routine portion of the system for controlling the applicationof a brake of a vehicle shown in FIG. 4; and

FIG. 6 is a block diagram illustrating in more detail a parameterestimation routine portion of the system for controlling the applicationof a brake of a vehicle shown in FIG. 4.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Referring first to FIG. 1, a disc brake 10 with a brake disc 12 whichcan rotate about an axis A and has internal venting is shown. A firstcarrier ring 14 is arranged an axial distance from the brake disc 12,parallel to the disc and coaxial with the axis A, there being mounted onthat side of the carrier ring which faces the brake disc 12 a pluralityof friction elements 16 which can be applied, in a manner explained inmore detail below, against the brake disc 12 in order to generate thefrictional force which is necessary to brake the brake disc 12. On theopposite side of the first carrier ring 14, facing away from the brakedisc 12, a series of wedges 18 are fixedly attached, each of whichdefines a first face 20 with an angle of inclination a and a second face22 with an angle of inclination β. Both faces 20, 22 of the firstcarrier ring 14 extend directly adjacently to one another, essentiallyin the circumferential direction of the carrier ring 14. In a modifiedembodiment (not illustrated here), the two faces 20, 22 do not abut oneanother at a common edge 24, as illustrated in FIG. 1, but instead havebetween them a section which extends parallel to the carrier ring 14.

As shown in FIG. 1, the two faces 20, 22 are inclined oppositely to oneanother, the angle of inclination β of the second face 22 beingsignificantly greater than the angle of inclination α of the first face20. The wedges 18, of which, for the sake of better clarity, only someare illustrated in FIG. 1, follow one another directly, viewed in thecircumferential direction of the carrier ring 14, so that the totalaxially outer face of the first carrier ring 14 is covered with wedges18. However, in other embodiments, which are not illustrated here, theremay be a certain distance between two successive wedges 18 in thecircumferential direction, and likewise the entire axially outer face ofthe carrier ring 14 does not need to be covered by wedges 18, butinstead the wedges 18 may be arranged, for example, in groups, therebeing a relatively large distance between two groups of wedges whichfollow one another in the circumferential direction. The wedges 18 maybe formed in one piece with the first carrier ring 14, but they may alsobe produced as separate parts and then fixedly connected to the carrierring 14.

Arranged axially outside the first carrier ring 14 is an annular bearingcarrier 26 with an approximately U-shaped cross-section which defines anannular cavity 28 which is open towards the carrier ring 14 and intowhich the wedges 18 project. A number of bearings 30, which correspondsto the number of wedges 18 and of which only two are illustrated in FIG.1, are rotatably mounted in this annular cavity 28. The axes of rotationof the bearings 30 which are provided to interact with the wedges 18 arealigned perpendicularly with respect to the axis A. In the exemplaryembodiment illustrated in FIG. 1, each bearing 30 is formed by a sleevewhich is rotatably mounted on an axis which is arranged fixed in termsof rotation in the bearing carrier 26.

An electric motor 32 is fastened on the radially inner circumferentialface of the bearing carrier 26, serves as an electric actuator for thedisc brake 10 and has an output pinion 34 which is in engagement withtoothing 36 formed on the radially inner circumference of the firstcarrier ring 14. If necessary, a gear mechanism (not illustrated) may bearranged between the electric motor 32 and the output pinion 34.

On the side of the brake disc 12 lying opposite the first carrier ring14 there is arranged, at an axial distance therefrom, a second carrierring 38, likewise parallel to the brake disc 12 and coaxial with theaxis A. This second carrier ring 38 is provided with friction elements16′ on its side facing the brake disc 12, which elements are mounted onthe second carrier ring 38 at points which correspond at leastessentially to the friction elements 16 and which also bear against thebrake disc 12 during the braking process.

Arranged in a radially outer region of the disc brake 10 are a pluralityof saddles 40 (three in this case) which engage over the bearing carrier26, the first carrier ring 14, the brake disc 12 and the second carrierring 38, and by way of radially inwardly projecting arms 42 aresupported, on the one hand, on the axially outer end face of the bearingcarrier 26 and, on the other hand, on the axially outer end face of thesecond carrier ring 38 or an element connected thereto.

The function of the illustrated disc brake 10 will now be explained, itbeing assumed that the disc brake 12 rotates in the direction of thearrow ω. This direction of rotation corresponds to forward travel in adisc brake 10 installed in a vehicle. In order to initiate a brakingoperation, the electric motor 32 is energized, and subsequently drivesthe output pinion 34 through an angle θ (which represents the change inthe angular motor position) in such a way that the first carrier ring 14rotates through an angle φ in the direction of rotation ω with respectto the bearing carrier 26 which is fixed in terms of rotation. As aresult, the first faces 20 of the wedges 18 run up onto the associatedbearings 30, causing the first carrier ring 14 to be displaced axiallywith respect to the brake disc 12, so that the friction elements 16 cometo bear against the brake disc 12. The amount s of the axialdisplacement of the carrier ring 14 (and thus of the friction elements16) is determined according to the formula:s=φ/(2π*P)φ being the angle of rotation and P being the inclination of the firstface 20 which results from the angle of inclination α.

After the friction elements 16 have been applied to the brake disc 12,the resulting reaction force also brings about an axial displacement ofthe second carrier ring 38 with respect to the brake disc 12 via thefriction elements 16, the first carrier ring 14, the bearing carrier 26and the saddles 40, with the result that the friction elements 16′ arelikewise applied to the brake disc 12 (floating caliper principle)virtually without delay. The wedges 18 which interact with the bearings30 constitute a self-energization arrangement, i.e. the activation forcewhich is applied to the disc brake 10 by the electric motor 32 via theoutput pinion 34 is automatically amplified without further forces to beapplied from the outside.

In order to terminate a braking operation which has been initiated, theelectric motor 32 is driven in such a way that the output pinion 34rotates counter to the direction of travel during the activation, withthe result that the first carrier ring 14 is moved back into itsstarting position again, i.e. the first faces 20 of the wedges 18 run upagainst the bearing 30, and the carrier ring 14 moves axially away fromthe brake disc 12.

So that, for example, a vehicle can also be braked when reversing, thewedges 18 have the second face 22 with the angle of inclination β. Theangle of inclination β of these faces 22 can be selected to besignificantly greater than the angle of inclination α of the first faces20, since particularly high frictional forces are usually not requiredduring reversing. Although the angle of inclination β which is greaterthan the angle of inclination α results in an increased energyrequirement of the electric motor 32 when braking occurs during reversetravel, this fact does not have disadvantageous effects when brakingoccurs during reversing because normally only a low braking force isnecessary.

Therefore, if the brake disc 12 rotates counter to the arrow ω (reversetravel), it being possible to detect the change in the direction ofrotation, the first carrier ring 14 is rotated with the aid of theelectric motor 32 to such an extent that the second faces 22 run up ontothe bearing 30. The braking process then proceeds as described above.

As an alternative, it is also possible to carry out the brakingoperation during reverse travel by means of the first faces 20. For thispurpose, however, the electric motor 32 must have sufficient forceand/or torque reserves (in particular in the case of a wedge arrangementunder compression, i.e. with a large angle of inclination α), since thearrangement of wedges 18 and bearings 30 then acts in aself-deenergizing fashion, so that the electric motor 22 must completelyapply the necessary frictional force itself.

Referring now to FIG. 2, another embodiment of a brake system 10′suitable for use with the present invention is shown. A simplifiedschematic of the principle behind system 10′ is shown in FIG. 3. Asshown in FIG. 3, a brake disc 201 is rotating in the direction of anarrow 201′. A ramp plate 202 is provided with a brake pad 203 forbraking engagement with the brake disc 201 at will. The ramp plate 202is movably connected to a ramp bridge 204, which for the purpose of thissimple explanation can be regarded as fixed, by a connecting means 205,here illustrated as a line.

At their surfaces facing each other, the ramp plate 202 and the rampbridge 204 are provided with curved or straight ramps 202′ and 204′,respectively. A roller 206 is freely rotatable between the ramps 202′and 204′. In a rest position (or a position for a non-applied brake) theunit comprising the ramp plate 202 (with its brake pad 203), the roller206 and the ramp bridge 204 is held with the brake pad 203 at a smalldistance from the rotating brake disc 201 and with the roller 206 in the“bottoms” of the ramps 202′ and 204′.

For brake application, a control force which is substantially transverseto the brake disc 201 (or in other words substantially axial) is appliedon the ramp plate 202, in the shown case through the connecting means205 as indicated by its upper arrow, until contact between the brake pad203 and the disc 201 is established. By means of the friction force, theramp plate 202 is transferred to the left in the drawing, so that theroller 206 rolls up the relevant ramps 202′ and 204′ and an applicationforce is accomplished without applying any external brake force besidesthe control force. In other words the brake has a self-energizingeffect.

The application force may be controlled by the control force, which canbe positive or negative. This is indicated by the provision of also alower arrow on the connecting means 205, but is not further illustratedand described in connection with FIG. 3. If the brake disc 201 rotatesin the opposite direction, the arrangement will function in a similarway due to the provision of the respective double ramps 202′ and 204′.In the shown case the ramps 202′ and 204′ are curved, but they canalternatively be straight. By having a certain curvature of the ramps, adesired brake application characteristic can be obtained.

Referring now specifically to FIG. 2, the ramp bridge 204 of brake 10′is connected to the indicated caliper by means of two adjustment screws211 in two threaded bores in the ramp bridge 204. Two rollers 206 arearranged between ramps 202′ and 204′ on the ramp plate 202 and the rampbridge 204, respectively. Although it is not shown in FIG. 2 or FIG. 3,it may be advantageous for obtaining full control and a completelysynchronous movement of the rollers 206 (irrespective of their actualnumber) to provide a common roller cage for the rollers 206, especiallyfor curved ramps 202′ and 204′.

An electric motor 214 can rotate a motor rod 215 in either direction (asindicated by angle of rotation θ) over a rotational speed reducing gearbox 216. A bevel gear 217 supported by an arm 218 from the ramp bridge204 can be rotated by the rod 215 but is axially movable thereon by asplined engagement. The bevel gear 217 is in driving gear engagementwith a bevel gear disc 219 rotationally supported by the ramp bridge204. Eccentrically connected to the bevel gear disc 219 is a crank rod220 rotationally connected to the ramp plate 202.

By turning the bevel gear disc 219 in either direction by means of thebevel gear 217 from the motor 214 through the gear box 216, the axialposition s of the ramp plate 202 in relation to the ramp bridge 204 canbe set. In this case the control force is transmitted by the crank rod220. When a friction engagement between the brake pad 203 and the brakedisc 201 has been established, an application force amplification willbe accomplished by the rollers 206 climbing their ramps 202′ and 204′(thereby also causing a change in the axial position s of the ramp plate202 in relation to the ramp bridge 204) in response to the tangentialmovement of the ramp plate 202 caused by the friction engagement withthe brake disc 201. The application force may be accurately controlledby rotating the motor 214 in either direction.

The adjustment screws 211 have the purpose of adjusting the position ofthe ramp bridge 204 in relation to the wear of the brake pad 203 (and acorresponding brake pad on the opposite side of the brake disc 201). Thesynchronous rotation of the adjustment screws 211 is performed from thegear box 216 by a chain 221 in a way not further described.

In the force transmission from the motor 214 there may be provided anactive or passive brake means 214′ for the purpose of preventing themotor 214 from consuming current, when there is no command from thedriver of the vehicle or the control system of the brake to rotate themotor in any direction. The brake means 214′ accordingly has thefunction to keep the outgoing motor shaft non-rotatable, when the motor214 is not energized to rotate in either of its two rotationaldirections.

As discussed above, control based on feedback is critically necessary tostabilize the brake 10, 10′. Otherwise the self-energized brake 10, 10′may become unstable, resulting in uncontrollable braking (i.e., lockup).However, also as discussed above, controlling the electric actuator(i.e., motor 32, 214) based upon feedback indicative of the frictionalforce between the pads 16, 16′, 203 and the disc 12, 201 isdisadvantageous for a number of reasons. As such, the brake 10, 10′according to the present invention includes a brake controller 100 whichcontrols actuation of brake 10, 10′ via motor 32, 214 based upon theposition of one or more brake system components. The pertinent positionmay, for example, be the rotational position of motor 32, 214 (changesin which are represented by angle θ), the axial position of the brakepads 16, 203, brake pad carrier ring 14 and/or ramp plate 202 (changesin which are represented by dimension s), the rotational position ofbrake pad carrier ring 14 (changes in which are represented by angle φ),or the position (or change in position) of some other brake component.Of course, it should be immediately recognized by one skilled in the artthat the control scheme detailed below can be used with substantiallyany type of brake system, and is not limited to use with the particularbrake systems 10, 10′ described above. Thus, certain brake systems mayinclude additional displaceable elements other than described aboveand/or may not include certain of the displaceable elements describedabove (for example, some brake systems may include brake pad carrierswhich are not rotationally displaceable). What is important is thatbrake controller 100 controls actuation of brake 10, 10′ based upon theposition of one or more brake system components—the particular componentwhose position is used to control brake 10, 10′ is unimportant.

However, as described above, taking the backlash in the mechanicaltransmission into account in the control calculations is undesirable. Assuch, the preferred source of the feedback of the position signal isfrom a mechanical location in the transmission located between the motor32, 214 and the main source of the backlash. The motor position (e.g.,the rotational position of motor 32, 214) is an example of a signal froma preferred mechanical location. This will exclude the backlash from thefast position control loop 110 (described in more detail below). Alsowith this control strategy it is important to keep the backlash small,as the backlash will be a part of an open loop system (i.e., theremainder of control scheme 108). Hence by using the feedback from theposition signal in the control loop, as described above, the problemsassociated with backlash in the mechanical transmission are avoided. Afurther implication of this is that it removes restrictions on how todimension the self-energizing brake. By using the position signal asfeedback in the fast position control loop 110, it is possible todimension the self-energizing brake to take full advantage of theoptimal brake reinforcement. It can be dimensioned to operate in boththe self-releasing and the self-applying domains. Hence, energy optimalsolutions are possible.

Brake controller 100 receives commands 102 indicative of a desiredcontrolled position Pos^(C) for one or more brake components, and drivesmotor 32, 214 accordingly in order to achieve the desired position.Signals 104 indicative of the position of one or more system components,the velocity (i.e., rate of change of position over time—d/dt position)of one or more system components and/or the acceleration (i.e., rate ofchange of velocity over time—d/dt velocity) of one or more systemcomponents received from position, velocity and/or acceleration sensors106 may be used by brake controller 100 to ensure that the motor 32, 214is driven in order to achieved the desired position of the brakecomponent(s) whose position is being controlled. If velocity and/oracceleration signals are employed, such may be measured directly byvelocity and/or acceleration sensors, or may be calculated based uponmeasured position by position sensors.

Referring now to FIG. 4, an embodiment of an overall brake applicationcontrol scheme 108 in accordance with the present invention is shown. Itshould be understood that brake controller 100, position, velocityand/or acceleration sensors 106, signals 104 indicative of the positionof one or more system components, the velocity (i.e., rate of change ofposition over time—d/dt position) of one or more system componentsand/or the acceleration (i.e., rate of change of velocity over time—d/dtvelocity) of one or more system components and motor 32, 214 comprise afast position control loop 110 portion of overall control scheme 108 andfunction as described above.

In addition to fast inner control loop 110 for controlling the position(e.g. the rotational position of motor 32, 214, the axial position ofthe brake pads 16, 203, brake pad carrier ring 14 and/or ramp plate 202,the rotational position of brake pad carrier ring 14, or the position orchange in position of some other brake component) of the self-energizingelectric brake actuator, control scheme 108 also includes a commandconversion routine 112 and a parameter estimation routine 114. Thecommand conversion routine 112 receives primary commands 116 (usually inthe form of a commanded brake torque T_(B) ^(C)) from an operator input(e.g. a brake pedal) or from vehicle brake system (e.g., a brake controlsystem, an anti-lock braking system, a stability control system, etc.)and converts primary commands 116 into position indicative commands 102using properties of the brake actuator to perform the signal conversionas more fully described below.

Examples of parameters which may be used by command conversion routine112 in the signal conversion include the effective disc brake radiusR_(eff), the disc/pad friction μ, the brake actuator elasticity c_(E),and the slack position Pos₀. One or more of these parameters may beestimated by parameter estimation routine 114 so that the estimatedparameters 118 may adapt to changes in the system. Such estimations maybe based on signals 104 indicative of the position of one or more systemcomponents and/or the velocity of the disc 12, 201 and/or the vehiclereceived from position and/or velocity sensors 106, and/or on additionalsignals 120 indicative of other system conditions received from one ormore additional sensors 122 as more fully described below. Since theseparameters changes relative slow, the parameter estimation learningworks on a slow time-scale. The control scheme 108 thus representsindirect position control of the brake 10, 10′.

Referring now to FIG. 5, operation of command conversion routine 112 isshown in greater detail. The primary commanded brake torque signal T_(B)^(C) is converted to an indirect commanded position signal Pos^(C). Itis also possible to have that primary commands 116 primary area alreadyin the form of commanded friction force F_(fric) ^(C), primary commandedclamping force F^(C) _(Clamping) or primary commanded position signalsPos^(C). In these cases only partial conversion or no conversion at allis required.

The physics of disc braking is employed by command conversion routine112 to convert the primary commanded brake torque signal T_(B) ^(C) to acommanded position signal Pos^(C). The commanded friction force F_(fric)^(C) is calculated at block 124 by dividing the commanded brake torqueT_(B) ^(C) with the effective disc brake radius R_(eff). The commandedclamping force F^(C) _(clamping) is then calculated at block 126 bydividing the commanded friction force F_(fric) ^(C) by the estimateddisc/pad friction coefficient μ. The commanded position signal Pos^(C)is calculated at block 128 by using the estimated brake padposition/force relationship Pos=f(F_(Clamping)) (shown in graph 130).This relationship is in general non-linear. A simplification is tocalculate the commanded position signal Pos^(C) by dividing thecommanded clamping force F_(Calliper) ^(C) by the estimated brakeelasticity c_(E) (total elasticity in the brake pad, caliper andtransmission), and adding the estimated slack position Pos₀.

Referring now to FIG. 6, operation of parameter estimation routine 114is shown in greater detail. The parameters needed to perform the commandsignal conversion are estimated based on sensor signals 104, 120 andmodels of the brake system 10, 10′. Since the parameters are changingslowly with time, it is acceptable that the parameter estimation routine114 run with a relatively slow learning rate. The position/clampingforce relationship (i.e., the parameters of brake elasticity c_(E) andslack position Pos₀) is estimated at block 132 using the a clampingforce signal (or optionally a friction force signal or a brake torquesignal) received from sensors 122 and the position signal 104 receivedfrom sensors 106. A number of known brake system parameters are used inthe estimation, as is known in the art. The estimation may be achievedusing known formulae and/or general functional relationships. The brakeelasticity c_(E) and slack position Pos₀ parameters are sent to commandconversion routine 112 and are used by parameter estimation routine 114at block 134 in order to estimate the friction coefficient μ. Also usedby parameter estimation routine 114 at block 134 in order to estimatethe friction coefficient μ are a motor current signal (or optionally amotor voltage or motor torque signal) received from sensors 122 and theposition signal 104 (or optionally a velocity or acceleration signal)received from sensors 106. A number of known brake system parameters areused in the estimation, as is known in the art. The estimation may beachieved using known formulae and/or general functional relationships.The friction coefficient μ parameter is sent to command conversionroutine 112. It should be noted that the effective disc brake radiusR_(eff) parameter may be provided to command conversion routine 112 byparameter estimation routine 114, or because it is substantiallyconstant may be maintained in a memory at command conversion routine112.

The present invention, therefore, provides a system for controllingapplication of an electronically controlled brake which is well-suitedfor controlling the application of an electromechanical brake withself-energizing characteristics, which facilitates the stability of aself-energizing brake for all possible disc/pad friction coefficients,which achieves the correct commanded torque/force on all brakes on thevehicle, which relies on sensor feedback to control application of thebrake, which relies on sensor feedback indicative of other than thefrictional force between the disc and pad, clamping force of the caliperor brake torque, which is not substantially deleteriously affected by adisc which has a thickness that varies during a revolution, which is notsubstantially deleteriously affected by ageing and corrosion of thesliding pins in a floating caliper design, and which does not take intoaccount backlash in the mechanical transmission in control calculations.

Although the invention has been described with reference to a particulararrangement of parts, features and the like, these are not intended toexhaust all possible arrangements or features, and indeed many othermodifications and variations will be ascertainable to those of skill inthe art.

1. A vehicle brake system comprising: a brake actuator; a brakecontroller operative to control said brake actuator; at least oneposition sensor which senses a current position of at least one moveablebrake component and provides a current position signal indicative of thecurrent position of the at least one moveable brake component to saidbrake controller; wherein said brake controller is operative to causeapplication of said brake actuator based at least in part upon acomparison of a position indicative command received by said brakecontroller, said position indicative command indicative of a commandedposition to which the at least one moveable brake component is to bemoved in order to achieve a demanded level of braking indicated by acommanded brake torque, with the current position signal; and a commandconverter which converts the commanded brake torque into a commandedfriction force by dividing the commanded brake torque with an effectivedisc brake radius, which converts the commanded friction force into acommanded clamping force by dividing the commanded friction force by adisc/pad friction coefficient, and which converts the commanded clampingforce into the position indicative command either: (i) by employing aknown relationship between brake pad position versus clamping force, or(ii) by dividing the commanded clamping force by a brake elasticity andadding a slack position.
 2. The system of claim 1 wherein said brakeactuator comprises a self-energizing brake actuator.
 3. The system ofclaim 1 wherein said brake actuator comprises an electromechanical brakeactuator, actuation of which is at least partially achieved employing anelectric motor.
 4. The system of claim 3 wherein the at least onemoveable brake component comprises an output shaft of the electricmotor.
 5. The system of claim 4 wherein the output shaft is rotatablymoveable, wherein the current position signal is indicative of a currentrotational position of the output shaft, and wherein the positionindicative command is indicative of a commanded rotational position ofthe output shaft.
 6. The system of claim 1 wherein the at least onemoveable brake component comprises at least one of a brake pad and abrake pad carrier.
 7. The system of claim 6 wherein the at least one ofa brake pad and a brake pad carrier is axially moveable, wherein thecurrent position signal is indicative of a current axial position of theat least one of a brake pad and a brake pad carrier, and wherein theposition indicative command is indicative of a commanded axial positionof the at least one of a brake pad and a brake pad carrier.
 8. Thesystem of claim 1 further comprising a parameter estimator forestimating, based upon sensor input, at least one parameter used by thecommand converter, and for supplying the estimated parameter to thecommand converter.
 9. The system of claim 8 wherein the at least oneparameter comprises at least one of an effective disc brake radiusparameter, a pad/disc coefficient of friction parameter, a brakeelasticity parameter, and a slack position parameter.
 10. The system ofclaim 8 wherein the sensor input is indicative of at least one of thefollowing: a clamping force, a friction force, a brake torque, thecurrent position of the at least one moveable brake component, avelocity of a brake disc, an acceleration of a brake disc, a motorcurrent, a motor voltage and a motor torque.
 11. A vehicle brake systemcomprising: an electromechanical self-energizing brake actuator,actuation of which is at least partially achieved employing an electricmotor; a brake controller operative to control said brake actuator; atleast one position sensor which senses a current position of at leastone moveable brake component and provides a current position signalindicative of the current position of the at least one moveable brakecomponent to said brake controller; a command converter for determininga position indicative command, said position indicative commandindicative of a commanded position to which the at least one moveablebrake component is to be moved in order to achieve a demanded level ofbraking indicated by a commanded brake torque, and providing theposition indicative command to said brake controller, wherein saidcommand converter converts the commanded brake torque into a commandedfriction force by dividing the commanded brake torque with an effectivedisc brake radius, converts the commanded friction force into acommanded clamping force by dividing the commanded friction force by adisc/pad friction coefficient, and converts the commanded clamping forceinto the position indicative command either: (i) by employing a knownrelationship between brake pad position versus clamping force, or (ii)by dividing the commanded clamping force by a brake elasticity andadding a slack position; a parameter estimator for estimating, basedupon sensor input, at least one parameter used by said commandconverter, and for supplying the estimated parameter to said commandconverter; and wherein said brake controller is operative to causeapplication of said brake actuator based at least in part upon acomparison of the position indicative command received by said brakecontroller with the current position signal.
 12. The system of claim 11wherein the at least one moveable brake component comprises an outputshaft of the electric motor.
 13. The system of claim 12 wherein theoutput shaft is rotatably moveable, wherein the current position signalis indicative of a current rotational position of the output shaft, andwherein the position indicative command is indicative of a commandedrotational position of the output shaft.
 14. The system of claim 11wherein the at least one moveable brake component comprises at least oneof a brake pad and a brake pad carrier.
 15. The system of claim 14wherein the at least one of a brake pad and a brake pad carrier isaxially moveable, wherein the current position signal is indicative of acurrent axial position of the at least one of a brake pad and a brakepad carrier, and wherein the position indicative command is indicativeof a commanded axial position of the at least one of a brake pad and abrake pad carrier.
 16. The system of claim 11 wherein the at least oneparameter comprises at least one of an effective disc brake radiusparameter, a pad/disc coefficient of friction parameter, a brakeelasticity parameter, and a slack position parameter.
 17. The system ofclaim 16 wherein the sensor input is indicative of at least one of thefollowing: a clamping force, a friction force, a brake torque, thecurrent position of the at least one moveable brake component, avelocity of a brake disc, an acceleration of a brake disc, a current ofthe motor, a voltage of the motor and a torque of the motor.
 18. Amethod of controlling a vehicle brake, said method comprising the stepsof: receiving a current position signal indicative of a current positionof at least one moveable brake component from a position sensor;receiving an indication of a commanded brake torque indicative ofdemanded level of braking; converting the commanded brake torque into acommanded friction force by dividing the commanded brake torque with aneffective disc brake radius; converting the commanded friction forceinto a commanded clamping force by dividing the commanded friction forceby a disc/pad friction coefficient, converting the commanded clampingforce into a position indicative command either: (i) by employing aknown relationship between brake pad position versus clamping force, or(ii) by dividing the commanded clamping force by a brake elasticity andadding a slack position; comparing the position indicative command withthe current position signal; and causing application of a brake actuatorbased at least in part upon the comparison between the positionindicative command and the current position signal.
 19. The method ofclaim 18 wherein the brake actuator comprises a self-energizing brakeactuator.
 20. The method of claim 18 wherein the brake actuatorcomprises an electromechanical brake actuator, actuation of which is atleast partially achieved employing an electric motor.
 21. The method ofclaim 20 wherein the at least one moveable brake component comprises anoutput shaft of the electric motor.
 22. The method of claim 21 whereinthe output shaft is rotatably moveable, wherein the current positionsignal is indicative of a current rotational position of the outputshaft, and wherein the position indicative command is indicative of acommanded rotational position of the output shaft.
 23. The method ofclaim 18 wherein the at least one moveable brake component comprises atleast one of a brake pad and a brake pad carrier.
 24. The method ofclaim 23 wherein the at least one of a brake pad and a brake pad carrieris axially moveable, wherein the current position signal is indicativeof a current axial position of the at least one of a brake pad and abrake pad carrier, and wherein the position indicative command isindicative of a commanded axial position of the at least one of a brakepad and a brake pad carrier.
 25. The method of claim 18 furthercomprising the step of estimating, based upon sensor input, at least oneparameter used during said converting steps.
 26. The method of claim 25wherein the at least one parameter comprises at least one of aneffective disc brake radius parameter, a pad/disc coefficient offriction parameter, a brake elasticity parameter, and a slack positionparameter.
 27. The method of claim 25 wherein the sensor input isindicative of at least one of the following: a clamping force, afriction force, a brake torque, the current position of the at least onemoveable brake component, a velocity of a brake disc, an acceleration ofa brake disc, a motor current, a motor voltage and a motor torque.
 28. Amethod of controlling a vehicle brake, said method comprising the stepsof: receiving an indication of a commanded brake torque indicative of ademanded level of braking; converting the commanded brake torque into acommanded friction force by dividing the commanded brake torque with aneffective disc brake radius; converting the commanded friction forceinto a commanded clamping force by dividing the commanded friction forceby a disc/pad friction coefficient, converting the commanded clampingforce into a position indicative command either: (i) by employing aknown relationship between brake pad position versus clamping force, or(ii) by dividing the commanded clamping force by a brake elasticity andadding a slack position; estimating, based upon sensor input, at leastone parameter used during said converting steps; receiving a currentposition signal indicative of a current position of the at least onemoveable brake component from a position sensor; comparing the positionindicative command with the current position signal; and causingapplication of a self-energizing brake actuator based at least in partupon the comparison between the position indicative command and thecurrent position signal.
 29. The method of claim 28 wherein the brakeactuator comprises an electromechanical brake actuator, actuation ofwhich is at least partially achieved employing an electric motor. 30.The method of claim 29 wherein the at least one moveable brake componentcomprises an output shaft of the electric motor.
 31. The method of claim30 wherein the output shaft is rotatably moveable, wherein the currentposition signal is indicative of a current rotational position of theoutput shaft, and wherein the position indicative command is indicativeof a commanded rotational position of the output shaft.
 32. The methodof claim 28 wherein the at least one moveable brake component comprisesat least one of a brake pad and a brake pad carrier.
 33. The method ofclaim 32 wherein the at least one of a brake pad and a brake pad carrieris axially moveable, wherein the current position signal is indicativeof a current axial position of the at least one of a brake pad and abrake pad carrier, and wherein the position indicative command isindicative of a commanded axial position of the at least one of a brakepad and a brake pad carrier.
 34. The method of claim 28 wherein the atleast one parameter comprises at least one of an effective disc brakeradius parameter, a pad/disc coefficient of friction parameter, a brakeelasticity parameter, and a slack position parameter.
 35. The method ofclaim 28 wherein the sensor input is indicative of at least one of thefollowing: a clamping force, a friction force, a brake torque, thecurrent position of the at least one moveable brake component, avelocity of a brake disc, an acceleration of a brake disc, a motorcurrent, a motor voltage and a motor torque.